A Case of Primary Alveolar Hypoventilation Syndrome

Abstract

A 56 year-old woman with primary alveolar hypoventilation syndrome associated with mild proximal myopathy was reported. Examination on admission revealed cyanosis, somnolence, cardiomegaly, moderate diaphragmatic elevation, signs of right-sided heart failure, pulmonary hypertension and polycythemia (RBC; 683×10⁴/mm³). Arterial blood gas analysis revealed a state of chronic respiratory acidosis, PaO₂ 46 Torr, PaCO₂ 65 Torr, and pH 7.40. After hyperventilation with room air, these values improved to PaO₂ 64 Torr, PaCO₂ 42 Torr, and pH 7.56 which indicated the presence of alveolar hypoventilation at rest, partially ameliorated by voluntary effort. Lung function tests showed a restrictive defect more likely to be caused by muscle weakness of the diaphragm than pulmonary disease. She showed blunted ventilatory responses to either carbon dioxide or simple hypoxia, but combined hypoxia and hypercapnia caused a powerful synergistic effect on ventilatory responses. The administration of 100% oxygen was followed by a paradoxical increase in minute ventilation as well as an improvement in blood gas pictures which were explained by, so called, “medullary depression” during room air breathing. The analysis of sleep stage showed that the amount of stage I was more than half of total sleep time (67%) and the amount of slow wave sleep and REM sleep were decreased. (SWS; 5%, REM; 2%) This fact was considered to be related to somnolence during the daytime. In this case sleep was associated with severe hypoxemia. Nocturnal administration of O₂ was an effective treatment of this case because the amount of stage I was decreased to 42 percent and the REM stage was slightly increased up to 5% and overall oxygen saturation level was elevated. Aminophylline was effective on the respiratory center during sleep because its administration decreased duration of periodic change in oxygen saturation with improvement of oxygen saturation.